office product key

If the product key was already redeemed before the laptop was flashed, the key is usually no longer needed. The Office license is typically linked to the Microsoft account that was used when Office was first activated.

Try this:

1. Go to the Services & subscriptions page and sign in with the Microsoft account that was used to buy or activate Office.
2. Check whether the Office product appears there.
3. If it appears, reinstall Office from that page.
4. When an Office app asks for activation, sign in with that same Microsoft account instead of entering the product key.

Important points:

• If Office shows “This product key has already been used”, that usually means the key was already redeemed and added to the Microsoft account.
• The full product key cannot be viewed in Office or online for most versions.
• In an installed Office app, the account tied to Office can be checked in File > Account under Belongs to.
• If the key was lost or damaged but there is valid proof of purchase, Microsoft support may be able to help with replacement options.
• If the product key was bought separately from the software and no longer works, the guidance is to contact the seller and request a refund.

References:

• "This product key has already been used" error in Office | Microsoft Support
• Using product keys with Microsoft 365 | Microsoft Support